In wireless communication technology, cooperative communication has been a popular research subject. In particular, a relay-assisted system has attracted much attention as one of the important research topics. Traditionally, in a one-way relay system with two terminals, only one terminal is allowed to transmit or receive signals (one way) at one point in time, so four time slots are needed to accomplish an information exchange between the two terminals via the relay. On the other hand, a two-way relay system allows two terminals to transmit signals to the relay simultaneously, and then the superimposed signal is broadcasted by the relay to the two terminals. Hence, only two time slots are required to accomplish an information exchange via the relay, effectively improving the spectrum utilization efficiency of the conventional one-way relay systems.
Although a two-way relay system provides better efficiency in spectrum utilization, the design of a corresponding relay precoder is generally more challenging. An iterative method, for example, is a strategy that provides the optimum performance at the cost of high design complexity. Currently, there are methods that reduce the design complexity of such precoders, for example, by using generalized singular value decomposition (GSVD) to diagonalize the effective multiple-input multiple output (MIMO) channels in the two-way relay system, or by designing a relay precoder with performance close to that of the iterative method using Gram-Schmidt orthogonalization. However, such low-complexity relay precoders are either unable to deliver sufficient performance or strictly limited in the number of antennas in the operating environment. Therefore, there is a need for a solution that addresses the aforementioned issues in the prior art.